The doctrine of prosecution history estoppel, also known as file wrapper estoppel, renders any correspondence with a government examiner during the prosecution of a patent application admissible in construing the claims of a granted patent. The concept of file wrapper estoppel exists in U.S. patent law. However, the Supreme Court of Canada in Free World Trust v. Électro Santé Inc., 2000 SCC 66, held that extrinsic evidence, including the prosecution history, is not admissible to construe patent claims in Canada.

In Pollard Banknote Limited v. BABN Technologies Corp., 2016 FC 883, the Federal Court reluctantly followed the Supreme Court’s ruling that file wrapper estoppel is not admissible in claim construction. Although the Federal Court followed the Supreme Court in Free World Trust, Justice Locke suggested that given the technological advances to-date, in particular that prosecution histories are now made available on the Internet, it may be time to revisit the relevancy of extrinsic evidence in claim construction. The admissibility of such evidence is particularly important in this case, as the patentee’s position on the construction of the claims in litigation appears to be directly contrary to the position taken before the patent office during prosecution of the application, and Justice Locke noted that the patentee’s argument likely would never have made it to trial in the U.S. where the doctrine of file wrapper estoppel applies (at para. 238). As of today’s date, an appeal to the Federal Court of Appeal has not been launched. See full decision here.